Obstructive sleep apnea syndrome (OSAS) is a common and serious cause of morbidity during childhood OSAS is characterized by recurrent episodes of partial or complete airway obstruction resulting in hypoxemia hypercapnea, and/or respiratory arousal. The sleep fragmentation and gas exchange abnormalities observed with OSAS may produce serious cardiovascular and neurobehavioral impairment. Habitual snoring is reported in 3-12% of the general pediatric population, although only 1-3% will have OSAS. The anatomical and/ol neuromuscular basis of the primary snoring (PS) and OSAS phenotype has not been elucidated. Upper airway patency is maintained by an intricate balance between the static pharyngeal mechanics, neuromuscular activity, and luminal pressure. A prominent role for upper airway neuromuscular control mechanisms in the pathophysiology of OSAS is hypothesized to explain the observation that obstruction does not occur while awake and is infrequently seen during NREM sleep. Using a validated intra-oral surface electrode to record genioglossus activity (EMGgg) and a nasal mask technique for measuring airway collapsibility (Pcrit), we will assess children with OSAS, PS and normal controls, awake and asleep, for the following; 1) Basal tonic and phasic EMGgg activity as a percentage of maximal; 2) Muscle and airway mechanical responses to hypercapnea (chemoresponsiveness); 3) Muscle and airway mechanical responses to continuous positive airway pressure (CPAP) and pulses of negative airway luminal pressure (mechanoresponsiveness); 4) Muscle and airway mechanical responses to inspiratory resistance loading. These studies address the role of neuromuscular compensatory mechanisms in the maintenance of airway patency during wakefulness and sleep in children. This proposal for a Mentored Patient-Oriented Research Career Development Award will permit the applicant to pursue his goal to become a clinical scientist. This training is set in the rich intellectual environment provided by the airway physiology laboratory of Dr. David P. White at Brigham and Women's Hospital, the Division of Respiratory Diseases at Children's Hospital Boston and the Harvard School of Public Health.